Apparatus for making bore holes



March 5, 1935. c, J. cs. AARTs ET AL APPARATUS FOR MAKING BOREHOLES 3Sheets-Sheet 1` Filed March 15, 1933 March 5, 1935. c. J. G. AARTs ET ALAPPARATUS FOR MAKING BORE HOLES Filed March l5, 1933 5 Sheets-Sheet 2F/6:3 F76 :4 F/6;5

March 5, 1935. c.l J. G. AARTs Er Al. 1,993,642

APPARATUS FOR MAKING BORE HOLES Filed March l5, 1933 3 Sheets-Sheet 3F7615 F/G.- 7

Patented Mar. 5, 1935 UNITED STATES PATENT OFFICE APPARATUS FOR MAKINGBOBE HOLES Application March 15, 1933, Serial No. 660,959 InGermanyMarch 19, 1932 20 Claims.

` The present invention relates to apparatus for making bore holes andmore particularly has reference to apparatus for melting the earthstrata or rock in which the bore hole is to be -formed and eitherremoving the kmolten mass or forcing it into the surrounding material toform a bore hole.

An object of this invention is to provide an apparatus for applying anintense heat to the material in which the bore hole is to be made.

Another object of the invention is to providey an apparatus for applyingan intense heat to the material in which the bore hole is to be formedand for enclosing the point of application of the heat to maintainthevmaterial which is melted under pressure.

Yet another object of the invention is to provide apparatus for makingbore holes by melting the material in which thebore hole is to beformed, which includes means for continuously or intermittently removingslag from the bore hole.

Still another object of the invention is to provide on the top of thebore hole a pressure-resisting chamber from which the bore hole ex-Vtends downward.

A further object is to provide means for lift-` ing and lowering theelectrical heating conductors and a slag exhaust tube through the coverof the pressure-resisting chamber at the top of the bore hole.

With these and other important objects in view, which may be incident tobur improve-L ments, the invention resides in the parts andvv earth orother material in which the bore hole y is to be formed. Through the topof this chamber extend conductors for conveying electric energy to theelectrodes or heating elements for applying heat to melt the material inwhich the bore hole is to be formed. These conductors may be loweredthrough the top of the chamber as the bore progresses downwardly. A tubeis provided which may be lowered similarly to the electrical conductors,so that its lower end will be in the molten material. The upper end ofthis tube is connected to reservoirs in which slag may 'be separatedfrom the gases. Other means are provided for vpurifying the partiallyseparated gases and returning them to the bore hole directly or throughthe slag removing tube. It is also contemplated to reinforce thematerial surrounding the upper portion of the bore hole to permit thedesired pressures to be maintained in the hole.

In order to make our invention more clearly understood, we have shown inthe accompanying drawings means for carrying the same into prac# ticaleffect without limiting the improvements in their useful applications tothe particular con structions which, for the'purposesfof explanation,have been made the subject of illustration.`

In the drawings:

Figure 1 is a more or less diagrammatic view, partly in section, of acomplete plant for making deep bore holes according to one form of thisinvention.

Fig. 2 is an enlarged fragmentary sectional View taken through thepressure-resisting top `chamber of the bore hole.

Fig. 3 is a vertical sectional view taken through the cover of the topchamber of the bore hole and part of the electrodes, the exhaust tubeand the device for extending the exhaust tube.

Figs. 4 and 5 are detail views, partly in section, of the exhaust tubeand the extending device in different positions.

Fig. 6 is a vertical sectional view of a somev what diagrammaticalapparatus showing another form of pressure top chamber connected withthe bore hole proper.

Fig. 7 is a fragmentary vertical sectional view of a part of the borehole showing in detail a device to ensure the relative position of thepending conductors.

Fig. 8 is a side view of a device which may be used for removingmaterial from the bore hole, if no exhaust tube is used.

Fig. 9 is a vertical sectional view taken through the lower part of thebore hole made with one form of apparatus according to this invention.In Fig. 1 of the drawings, a fragmentary sectional view of a bore holeis shown being drilled in accordance with the present invention withapparatus suitable for the purpose. As is known,

rock or other siliceous material is a non-conductor for electricity whenin the solid state, but when heated to a molten state it becomesconductive and is maintained in the molten state by the heating effectof the electrical current invention contemplates the formation andprovision of a pool of, molten rock or othermaterial over the spot inwhich the bore hole is formed. To this end, a plurality of tungstenelectrodes are positioned in spaced apart relation in a pool of moltenslag. The heating, in accordance with this invention, is effected by thepassage of electrical energy between the electrodes 5, which areimmersed in spaced apart relation in the molten pool of slag 36.

Ihe molten slag generally hasa resistance of the order of 1 ohm for adistance of thev electrodes of cm., so that it is easy to provide alarge amount of energy in the small space of the molten slag. To preventheat losses and to protect the current conductors against radiant heat,a refractory sheet 38 is provided a little above the the highest levelof the slag through which the electrodes pass and which may be composedof zirconium oxide, quartz or other -refractory material.

Electrical energy is supplied to the electrodes 5 by means of conductors4 which are suspended from a structure above the surface in which thehole is to be formed. Preferably the conductors 4 are wound on drums sothat the electrodes may be lowered as the boring process proceeds.

In Fig. 1 the electrodes are shown connected to a three-phasealternating current supply system. In this instance, there are threeelectrodes which are spaced equidistantly apart to obtain the bestheating eil'ect in the pool of molten material. Of course, as shown inFig. 6 a two electrode system may be employed.

The electrodes 5 are connected to the conductors 4 by connections 6 ofmolybdenum or nickel. In the beginning of the boring or after replacingthe electrodes by new ones, it is necessary to provide a pool of moltenslag so that the electric current will flow between the electrodes. Forthis purpose, the electrodes may be connected by a resistance wire ofnichrome embedded in an easily fusible substance, such as glass powder.'Ihe resistance wire is brought to incandescence and causes the meltingof the glass. 'I'he glass becomes conductive and forms an electricallyconductive slag in which the elec--A trodes are immersed. Ihe meltingthus started maintains itself.

The boring action is carried out by applying a pressure above the poolof molten material. As shown in Fig. 1, this is eiIected by positioninga pressure top chamber 3 over the hole. An`

intermediate reinforcing structure 2 is shown to prevent the pressureleaking between the chamber and the material in which the bore is made.

Chamber 3 has openings formed in its top through which the conductors 4extend. As shown in detail in Fig. 2, tubes 'l are slidably iltted inthe openings provided in the top of chamber 3 and the conductors 4 arepassed through the tubes 7. A gland stuillng box 8 is provided at lowerends of the tubes 'l to prevent leakage of gases between the tubes 7 andthe conductors 4. Similarly, gland stufnng boxes 9 are provided toprevent leakage between the top of chamber 3 and the tubes 7. Y

The lowering of the electrodes in the bore hole is effected by loweringthe tubes 7. However,

as soon as the upper end of tubes 7 comes near 'to the gland 9, theconductor 4 can be retained in its position by clamping means 33 withinthe top chamber which may be controlled from the outside, so that thetubes 'l can be lifted up without lifting the conductor. As soon as thetube 7 is again in its highest position, the clamping means 33 areremoved and the tube with a conductor can be lowered uniformly.

The pressure top chamber 3 is provided with a gate valve 32 which may beshut if the electrodes 5 and tube 10 are lifted up above said valve, forinstance, if new electrodes are needed. When the valve 32 is closed, thepressure in the bore hole is maintained and the cover ofthe chamber 3may then be removed and the electrodes or the ejector removed andreplaced, if desired. Of course, conductors 4 must be electricallyinsulated from the top of chamber 3.

Since the boring is carried out under pressure, a part of the moltenrock or other material is forced into the more or less poroussurrounding strata. The wall 1 of the bore is formed of the hardenedmolten material. As the depth of the bore is increased, it becomesnecessary to remove a portion of the pool of molten material so that theapplication of heat can be more concentrated. This inventioncontemplates the removal of the molten slag by passing a current of gasup through a tube and aspirating slag into the upilowing gas stream.

For this purpose, a tube 10 is provided having an ejector connected toits lower end, i. e., the tube 10 is connected to a small tube ofrefractory material open at its lower end and having small perforationsnear the place where it is connected to the tube 10 through which gasmay enter tube 10. If a rapid gas current ascends through tube 10, itaspirates the molten slag, atomizes it and lifts it in atomizedcondition upwards. The tube 10 discharges in a structure 11 whichalternatively may be connected by means of a three-way valve with one ofthe two high pressure chambers 12 and 13, in which the powder resultingfrom the atomized slag is deposited. The body 11 and the high pressurechambers are connected by a ilexible tube 14, which permits the body 11to be lifted and lowered without breaking the connection. .V

From the high pressure separating chamber 12 or 13, the gas passesthrough a valve 121 or 131 to the low pressure chamber 16. If one of thevalves 121 or 131 is opened, a gas current is established in tube 10 andtherefore exhaust of the slag takes place if one of these valves isperiodically opened. From the low pressure chamber 16, the gas passesthrough purifying means 17, 18 and 19 to the compressor 20. In 19 thegas is carried over red hot copper, in 18 carbon dioxide and part of thewater are removed, and in 17 the gas is completely dried. From thecompressor 20 the purified gas passes via the three-way cock 21, eitherthrough the conduit 22 directly into chamber 3, or by conduit 23,flexible conduit 14, body l1 and `tubelll again into the bore hole. Inthe lattercase, the tubes 14, l1 and 10 are blown out. I f desired, thecompressor, the purifying means and the high and low pressure chambersmay be mounted on a car.

As the depth of the bore is increased, it becomes necessary from time totime to increase The body 11 can be lifted and lowered together withtube 10, the latter sliding in the gland 27 in the cover of chamber3.'-When the bore hole becomes deeper, tube 10`is lowered more and moreand as it must slide through the gland 27 it must be of uniform diameterand must have a smooth surface. As the tube is elongated by screwing onnew parts, it is necessary to screw on a new part without releasing thepressure in the tube. For this purpose, the body 11 has a cock 28, andabove the cock 28 thebody 11 is provided with a flanged socket having agland 29 associated therewith. If the tube 10 must be elongated, a newpart is put in the socket above cock 28 and tightened by the gland 29.The new part of the tube is closed by a cap 30 on the upper side. Nowthe cock 28 is opened. The new part is lowered through body 11 andscrewed onto tube 10 in the chamber 25, without loss of gas due to theprovision of the gland 29. After the new part has been screwed onto tube10, the body 11 is lifted and slides over the tube until the gland 29touches the flange 31 of the cap 30. The cap 30 and the gland 29 are nowconnected to provide a gas-tight joint and the body 11 is lifted againuntil the end of tube 10 is separated from the cap 30 and its open endis within chamber 25. After cock 28 is shut, the cap 30 may be removedfrom the gland 29 and may be used again by putting it on a new part ofthe tube. The tube 10 is again rigidly connected with the body l1 bytightening gland 24, so that both can be moved downward together asrequired by the periodic removal of the molten slag. The abovedescribedoperation may be effected without the escape of gas.

Fig. 6 shows a modified construction of the chamber 3 which, at itslower end, is connected with a steel cylinder 40 by flanges 41 and bolts42. The cylinder 40 with the bolts 42 and the tube 43 are shown anchoredin a heavy block of concrete 45. Within the lower part of the cylinder40 extends a tube 43 which constitutes the beginning of the bore hole.'This tube consists preferably of a material having a small coeilcientof heat expansion, for instance, quartz or cement, which may be fused tothe underlying earth strata or rock.- Tightness between the cylinder 40and the tube 43 may be provided by means oi' a lead packing. If a gasunder pressure is admitted in the bore hole, it will exert a pressure onthe chamber 3 tending to lift it, but this pressure will be taken up bythe bolts 42v embedded in the block of concrete, so that the chamber 3and cylinder 40 cannot move with respect to the tube 43.

With this construction, the beginning of the boring takes place in tube43 in which the electrodes are lowered. If, in the beginning of theboring, the earth strata cannot withstand the highest pressure, whichwill be required in making the bore hole, the boring is rst effectedwith a lower pressure until strata of the desired resistances arereached. The part of the bore hole which is made without application ofthe maximum pressure may be reinforced by steel tubes 40, and thetightness between the wall of the bore hole and the steel tubes may beensured by pouring cement between said wall and the steel tubes 40. Thepart of the bore hole reinforced by the steel tubes and the steel tubesthemselves must have a sumcient diameter to let the electrodes, etc.,pass without touching them.

In order to ensure the distance between the free pending electrodes andto maintain generally the position of these electrodes and the tube 10with respect to each other and with respect to the wall of the bore holeas uniform as possible, distancing pieces 46 are provided at variousheights as shown in Fig. 7. 'I'hey consist preferably of electricalinsulating material, such as rubber, and they are so elastic that theyadhere to the conductors and the exhaust tube and therefore are loweredand lifted therewith but yet may slide over them. When the tube 10 andthe conductors 4 are lifted, the distancing pieces 46 are lifted untilthey reach the cover 48 which retains them until they all lay one on theother vwhen the electrodes are fully lifted.

In order to prevent the distancing pieces all being carried downtogether when the electrodes and tube 10 are lowered, a fork 49 isprovided which can be actuated in a manner similar to that of the valve32. As soon as the electrodes are lowered, the fork is put in a positionwithin the chamber 3 to retain the distancing pieces until theelectrodes are lowered over such a distance that a distancing piece isrequired. When the fork is withdrawn, the electrodes are lowered over adistance equal to the thickness of one distancing piece and the fork isagain forwarded to its retaining position. Thus, only one distancingpiece is lowered at a time with the electrodes. As soon as theelectrodes are again lowered over a sumcient distance, a seconddistancing piece is allowed to go down with them, etc.

Instead of removing the slag through tube 10, a hollow receptacle orchamber 50 may be lowered bodily into the bore hole for the collectionand removal of slag. As shown in Fig. 8, chamber 50 is connected to theend of a hollow cable 51 by means' of which it is lowered into andremoved from the bore hole. The lower end of chamber 50 is provided withan aspirating device 53 for causing slag to be sucked into the chamber50 by a stream of gas flowing from the bore into the chamber. Cable 51may be connected to a gas circulating and purifying system, such asshown in Fig. 1 and described in detail hereinbefore. The essentialdifference between removing slag by the means shown in Fig. 8 and by thetube 10 resides in the fact that the slag is retained in the chamber 50and is not carried up out of the hole by the circulating gas stream. Inorder to ensure that the aspirated slag will be maintained in chamber 50and will not flow up through conduit 51, a filter 52 is provided at theupper end.

When the chamber 50 is full, it can be raised bodily and removed fromthe bore hole. For this purpose, air locks (not shown) may be providedin thecover of pressure chamber 3 so that the slag,.chamber 50 may beremoved from and reintroduced into the bore hole without leakage of gasor loss of pressure. Cable 51 may be passed through the top of chamber 3similarly to the conductors 4 to avoid leakage of gas.

The present invention also contemplates the protection of the lower partof the electric conductors and the exhaust tube. In Fig. 9, the lowerends of conductors 69 and exhaust tube 71 are shown protected by arefractory cylindrical body 67. The electrodes 63 and the tube 64 passthrough the bottom of therefractory cylindrical body 67, the walls andthe'bottom proper 65 of which consist preferably of quartz (fusedsilica). Against the lower side of the bottom is applied 'a protectinglayer 66 of highly refractory material, such as zirconium oxide.

The tube 64 may be formed, for instance, of platinum tubing of a fewmillimeters diameter.

Within the body 67 this small tube has perforations 70, above which thetube is connected to an expanding tube 71 of other material. The gasenters in the tube through the perforations 70, aspirates the slag andatomizes it into the tube 71.

Within the body 67, the electrodes 63 are connected to intermediaryconnections 68 of nickel which are connected with the copper currentconductors 69. If the bore hole is filled with an inert gas or withhydrogen, the electrodes 63 may be made of tungsten or anotheroxidizable highly refractory metal or alloy. If, however, the bore holeis filled with an oxidizing gas, the electrodes should consist ofnon-oxidizable refractory conducting material, such as platinum or aplatinum rhodium alloy or the like, or they may consist of an oxidizablecore with a protecting cover of non-oxidizable material. This covershould extend at least as far as the electrodes extend out of the slagand may be in the form of a platinum jacket. In this case, it isnecessary to apply a substance, for instance, a silicate between theplatinum and the core to prevent contact between the platinum and thecore material (tungsten or the like) in order to avoid the formation ofalloys having a low melting point. The electrodes 63 extend a fewcentimeters below the tube 64 and deviate sufficiently from each otherto form a bore hole of sufficient diameter for the passage of the body67. As the tube 64 is in the center between the electrodes 63, a voltmeter connected with the slag exhaust tube will show the average voltagebetween the electrodes. This voltage remains constant as long as tube 64contacts with the molten slag 62. However, if this contact as may beexpected during the continued aspiration of the slag is continuallydisrupted, the volt meter will show this by a vibration and this willindicate that 'the slag is continually removed as desired, but if the'tube 64 is obstructed the voltmeter will show a constant voltagewithout vibration. This vibration may also be indicated by a telephone.

The gas introduced in the bore hole enters the cylindrical body 67 andcools the current conductors 69 and the intermediary connection 68before it enters into the perforations 70 in the platinum tube 64. Thegas escapes in the expanding tube 71, aspirating, atomizing and carryingwith it the slag. The body 67 is preferably made of fused silica becauseit is subjected to very different temperatures, namely, on one side tothe temperature of the relatively cool gas current and on the other sideto the radiation of the hot walls of the bore hole and the slag and thehigh temperature of the tube 64 and the electrodes 63.

The cylindrical body 67 affords a vvery good protection of the currentconductors andexhaust tube. For facilitating lifting of the body 67,which is necessary when the electrodes or the tube 64 must be repairedVor renewed, the conductors and the exhaust tube may be in the form ofcables which may be combined into a single cable. This ensures that theelectrodes and discharge tube may be lowered and lifted as a unit.Around the refractory body and between it and the molten slag theatmosphere is relatively undisturbed, which permits the gas to cool theexhaust tube and the conductors within the cylindrical body withouthaving an undesired cooling influence on the molten slag and the wallsof the bore hole.

The electrodes used for carrying out the present invention arepreferably made of tungsten or similar material, such as molybdenum,tantalum and carbides of refractory metals. In order to avoid oxidationof tungsten, which is strongly attacked by oxygen, water vapor or otheroxygen-containing gases, it is important that the gaseous atmospheremaintained in the bore hole be of a non-corroding nature. The gaseousatmosphere may, for instance, consist of nitrogen and/or hydrogen.

In place of the atmosphere of nitrogen and/or hydrogen, an atmosphere ofhydrocarbon gases may be used advantageously. For this purpose, liquidhydrocarbons may be introduced into the bore hole and by reason of thehigh temperature prevailing at the bottom thereof, the liquidhydrocarbons will be cracked, resulting in a deposition of carbon on thetungsten electrodes and the formation of free hydrogen, together withother light hydrocarbons. The carbon deposited on the electrodes forms aprotective coating which has no, or only a slight, action on thetungsten. Any oxygen present or formed adjacent the carboncoatedtungsten electrodes will be converted by the carbon coating into carbondioxide, thereby avoiding the direct action of oxygen on the metalelectrodes.

The use of cheap liquid hydrocarbons instead of expensive hydrogen orammonia gas makes it possible in many cases to dispense with thepuriiication and recovery of the gases circulated through the bore holeand which are used to carry the atomized slag upwardly out of the hole.In many cases, natural earth gases will be available and may be used toform the atmosphere Within the bore hole. It is also possible tointroduce gasolene or other liquid hydrocarbons I:

into the bore hole since the decomposition of these substances willyield a gas suitable for maintaining the required pressure. While thedecomposition of the hydrocarbons absorbs considerable heat which mustbe generated in and supplied to the bore hole as electrical energy, thisis not a serious drawback to the use of liquid hydrocarbons, since theuse of the same simplifles the process to such an extent as to justifythe heat losses, especially since electrical energy is now generallyavailable at low cost.

In many cases, it will be found advantageous to work with a mixture ofhydrogen and hydrocarbons, since such mixtures are generally low in oostand may be formed, for instance, by beginning the boring with purehydrogen or ammonia gas and adding hydrocarbons to make up for theunavoidable losses during operation and to take care of the increaseddepth of the bore hole.

From the foregoing description, it will be realized that the presentinvention is highly advantageous, since it provides for theconcentration of a large amount of heat at the bottom of the bore hole.By heating the bottom of the bore hole, not only is a molten slagobtained, but also the rock surrounding the bore hole becomes plasticand due to the pressure maintained in the bore hole is pressedoutwardly. An external pressure is exerted in the plastic material whichopposes the pressure in the bore hole'v and as the plastic materialbecomes gas-tight, an equilibrium will be set up and the bore hole willobtain a definite form. It is possible to drill the vbore hole inaccordance with the present invention without the use of anyreinforcement, except possibly near the surface where it may benecessary, due to the low external pressure surrounding the bore hole toprovide an intermediate reinforcing structure.

Since the electrodes are freely suspended, the

bore hole will be truly vertical and will be of the same diameterthroughout its depth. In accordance with the present invention, boreholes oi'v from 20 to 30 cm. in diameter of any desired depth may bemade. It will berealized that the present invention which permits theboring of' holes of such depth is highly advantageous over the prior artmethods in which the depth of the hole is nearly always limited by thefailure of the apparatus or the enormous expense entailed.' The boringin accordancer with the present invention Aproceeds very rapidly and asthe heat is applied to the material to be melted in a very eicientmanner, little energy is required to melt the material and therefore theprocess may be carried out at a much lower cost than is involved inanyof the known methods.

If several oil layers are passed during the drillingjit is possibletomake openings in the side wall of the bore hole, for instance, byfloating a layer of hydrouoric acid on a heavyV oil in the bore hole atthe proper level so that the acid acts on the wall to permit access tothe oil layer.

It is possible to enlarge the bottom part of the bore hole bymaintaining the electrodes a considerable time at the lowest point. Inthis way an enlargement at the bottom of the bore hole is obtainedwhich, after breaking of the Walls, ensures an easy flow of oil. It isalso possible to make such an enlargement of the bore hole inr placeswhere oil bearing strata occur. The composition of the strata throughIwhich the bore proceeds is indicated by the composition of the atomizedslag which is recovered in the dust chambers. Y

While in the foregoing description reference has been made to anapparatus in which three electrodes are used with a three-phasealternating current, it should be understood that any number ofelectrodes may be employed and that any kindof suitable electric currentmay be utilized for effecting the heating. For instance, two electrodessupplied with energy from a common alternating current supply line aresatisfactory.

The present invention is also advantageous in that a number of drawbacksof, the usual methods are avoided. For instance, the possibility ofwater flowing from one layer along the bore hole to an oil layer isavoided by reason ofthe hardened Wall of solidified molten material withwhich the bore hole is lined, being impervious to. the various layers of`oil and Water through which the bore is made. f

While we have shown and described the preferred embodiment of ourinvention, we wish it to be understood that we do not -conne ourselvesto the precise details herein set forth by way of illustration as it isapparent that many changes and variations may be made therein by thoseskilled in the art, without departing from the spirit `of the inventionor exceeding the scope of the appended claims.

What we claim is:

1. Apparatus for making bore holes comprising a pressure resisting topchamber on the top of the bore hole, means for building up a gaspressure in the bore hole, current conductors pending from said topchamber to near the bottom of the bore hole and highly refractoryelectrodes connected to the lower end of said conductors and capable ofdipping into the slag at the bottom of the bore hole.

2. Apparatus for making bore holes comprising a pressure resistingtop'chamber on the top of the bore hole, means for building up agas'pressure in the bore hole, current conductors pending from'saidtopchamber to near the bottom of the bore hole and tungsten electrodesconnected by an intermediary connection of less refractory metal to saidcurrent conductors.

3. Apparatus for making bore holes comprising a pressure resistingchamber on the top of the bore hole, means for building up a gaspressure in the bore hole, current conductors connected with electrodespending from said top chamber and tubes slidingly arranged in the coverof said topchamber through which the current conductors slidingly pass.

4. Apparatus according to claim 3, in which the top chamber containsclamping means controlled from outside by which the conductors may befastened, so that the tubes through which the conductors pass, may belifted or lowered without lifting or lowering the conductors.

5.L Apparatus for making bore holes comprising a pressure resisting topchamber on the top of the bore hole, means for building up a gaspressure in the bore hole, current conductors connected to electrodespending from said top chamber and a discharge tube open at its lower endextending through the entire bore hole and passing through the cover ofthe top chamber.

6. Apparatus for making bore holes comprising a' pressure resistingchamber on the top of the bore hole, means for building up a gaspressure in the bore hole, current conductors connected to electrodespending from said top chamber, a discharge tube open at its lower endextending through the bore hole and passing through the cover of the topchamber and distancing pieces sliding arranged between said conductorsand said discharge tube at various heights in the bore hole.

7. Apparatus for making bore holes comprising a pressure resistingchamber on the top of the bore hole, means for building up a gaspressure in the bore hole, current conductors connected to electrodespending from said top chamber, a discharge tube the lower end of whichis formed by an ejector consisting' of a narrow tube of highlyrefractory material adapted tor dip into the molten slag at the bottomof the bore hole and ing provided with a filter at its upper end and`with a highly refractory -ejector at its lower endA adapted to belowered into the molten slag.

9. Apparatus for making bore holes comprising a pressure resisting topchamber on the top of the bore hole, means for building up a'gaspressure in the bore hole, current conductors pending from said topchamber to near the bottom ofthe borehole, a discharge tube passingthrough the cover of said top chamben, the top chamber being providedwith a slide valve adapted to shut oft' the bore hole and maintain thepressure therein when the cover is removed from the top chamber.

l0. Apparatus for making bore holes comprising a pressure resisting topchamber on the top of the bore hole, means for building up a gaspressure in the bore hole, current conductorsy part tom of the bore holeand tungsten electrodes connected to the lower end of said conductors.

11. Apparatus for making bore holes comprising a pressure resisting topchamber on the top of the bore hole, means for building up a gaspressure in the bore hole, current conductors pending from said topchamber to near the bottom of the bore hole and electrodes of a highlyrefractory metal connected to the lower end of said electrodes, dippinginto the slag at the bottom of the bore hole and having a protectingcover against oxidation for so far they extend above the slag.

12. Apparatus for making bore holes comprising a pressure resisting topchamber on the top of the bore hole, means for building up a gaspressure in the bore hole, current conductors pending from said topchamber to near the bottom of the bore hole and electrodes of anon-oxidizable refractory metal connected to the lower end of saidconductors. I

13. Apparatus for making bore holes comprising a pressure resisting topchamber on the top of the bore hole, means for building up a gaspressure in the borehole, current lconductors pending from said topchamber to near the bottom of the bore hole and electrodes made of aplatinum rhodium alloy with 10% rhodium.

14. Apparatus for making bore holes comprising a pressure resistingchamber on the top of the bore hole, means for building up a gaspressure in the bore hole, current conductors pending from said topchamber to near the bottom of the bore hole and highly refractoryelectrodes, connected to the lower end of said conductors, a dischargetube open at its lower end extending through the entire bore hole andpassing through the cover of the top chamber and a refractorycylindrical body, provided with a bottom and surrounding the lower partof the current conductors and discharge tube, the electrodes and anejector of small diameter connected to the discharge tube passingthrough the bottom of the cylindrical body.

15. Apparatus according to claim 14, in which the electrodes deviatefrom each other after passing through the bottom of the cylindricalbody.

16. Apparatus for making bore holes comprising a pressure resistingchamber on the top of the bore hole, means for building up a gaspressure in the bore hole, current conductors pending from said topchamber to near the bottom of the bore hole, highly refractoryelectrodes, connected to the lower end of said conductors, a dischargetube open at its lower end extending through the entire bore hole andpassing through the cover of the top chamber and a refractorycylindrical body, provided with a bottom surrounding the lower of thecurrent conductors and discharge tube, the electrodes and an eiector ofsmall diameter connected to the discharge tube passing through thebottom of the cylindrical body in such manner that the electrodes extenda few centimeters lower than the ejector.

17. Apparatus for making bore holes comprising a pressure resistingchamber on the top of the bore hole, means for building up a gaspressure in the bore hole, current conductors pending from said topchamber to near the bottom of the bore hole, highly refractoryelectrodes, connected to the lower end of said conductors, a dischargetube open at its lower end extending through the entire bore hole andpassing through the cover of the top chamber and a refractorycylindrical body,provided with a bottom surrounding the lower part ofthe current conductors and discharge tube, the electrodes and an ejectorof small diameter connected to the discharge tube passing throughpthebottom of the cylindrical body, the electrodes and discharge tube beingso connected to said body that they may be lowered and lifted as a unit.

18. Apparatus for making bore holes comprising a pressure resistingchamber on the top of the bore hole, means for building up a gaspressure in the bore hole, current conductors pending from said topchamber to near the bottom of the bore hole, highly refractoryelectrodes, connected to the lower part of said conductors, a dischargetube open at its lower end extending through'the entire bore hole andpassing through the cover of the top chamber and a refractorycylindrical body, provided with a bottom surrounding the lower part ofthe current conductors and discharge tube, the electrodes and an ejectorof small diameter connected to the discharge tube passing through thebottom of the cylindrical body, the electrodes andI discharge tube beingconnected within a cable passing through the cover of the top chamber..

19, Apparatus for making bore holes comprising a pressure resistingchamber on the top of the bore hole, an intermediary structure connectedin a gas tight manner with said top chamber, and with the upper part ofthe bore hole, means for building up a gas pressure in the bore hole,current conductors pending from said top chamber to near the bottom ofthe bore hole.

20. Apparatus for making bore holes, comprising a pressure resistingchamber on the top of the bore hole, an intermediary structurecomprising a heavy block of the reinforced concrete between said topchamber at the beginning of the bore hole and tightly connected to saidtop chamber and to the bore hole, means for building up a gas pressurein the bore hole, current conductors connected to electrodes pendingfrom said top chamber to near the bottom of the bore hole in a dischargetube extending through the entire bore hole and passing through thecover of the top chamber.

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